Directly behind the valve cover between the motor and the firewall is
the plastic valve that sends hot coolant to the heater core.
If the 80/90 is the same as the 4000Q (85 - 87) then that's your
reason why your heat seems on.
Finger muscle on the lever with the wire attached and cool air to all vents.
HTH - Scott in BOSTON
A few things can cause this to happen in general. 1) the heater valve
may be bad/stuck open, allowing hot water to flow through the heater
core all the time. 2) A flapper control valve is not operating either
beause it is bad, or there is a vacuum leak.
I think that (1) is the problem, as on all the 4kqs I have if the heat
is on, then you get hot air through the side vents, and I AFAIK cold
air through the center - all the time. If there is no hot water
circulating through the core, then the side air vents will be cool(er).